Posts by Mike5000

    Hi DB8TF yes your sw drift corr is a cool idea. However you are dependent on the cw beacon always being available ( they have turned it off one time already as far as I know).


    Many times people also transmit (almost) on top of the cw beacon to check their power level and frequency etc. This can cause problems with such a scheme if the FFT peak selector algorithm of yours locks onto the wrong FFT bin because the guy sending almost ontop of the beacon is stronger etc etc etc


    (I took a quick look at your .py code. Cool concept for sure). Also not always do we have the possibility for cat control of the receiver.


    That's why I at least for now would like a hw based approach.

    OK sure this makes it less mechanically complicated, but wouldn't the 2,4Ghz TX efficiency be affected by that metal bar inside?


    0dbW (1W) into 26dB gain (dish) will give 26dBW out (I assume feed gain is already included in the dish gain .. this may be incorrect).


    14dbW (30W) into 18dB gain (25t helix) will give 32dBW out. (More than you should need to have equal signal level on the sat it appears)


    The gain difference between the two antenna gains should be 26dB - 18dB = 8dB.

    If true, that would mean you would only need 8dB more power on the helix to have the same signal as with the dish using 1W. Not 40W.


    You would only need to go to approx 8W (this is 9dB for the ease of calculation so you wouldnt even need 8W) on the helix to have the same power reaching the RX in the sat as from the parabolic dish with 1W in?


    You should have been approx 6 dB stronger when using the Helix with 30W. If that is the case, then the helix seems to be affected in some way?


    Note: my calculations may be incorrect.

    DD0KP sure thanks for info. However, I would then need a directional coupler and a generator capable of generating RF at 2,4 GHz.


    I in fact do have a -30dB directional coupler that works up to well above 2,4Ghz so I could use that. However since the MDS of the AD8362 is -52dBm (according to the datasheet), I would need to generate at least -22 dBm plus say a safety margin to improve detection noise of +10 dB. So I would assume a -12dBm generator should be ok. That generator should be sweepable. I guess the output of that detector could be fed to a uC or an analog display.


    So the next question is: does a cheap module that can generate at least -12dBm at 2,4 GHz exist?

    I have tested now 4 different LNBs (WITH PLL, not the type with DRO as they drift even more).


    All of the LNBs with PLL drifts a lot, so all needs to be modified for any serious downlink work at least.


    Unless you like to adjust the VFO every 10 seconds or so. There also seems to be some short term drift / wobbling.

    It seems that the signal level compared to the noisefloor of the transponder are weaker than the first days. Have there been made any gain adjustments or similar on the satellite transponder lately?

    I am looking for a SWR meter for adjusting 2,4 GHz TX antennas for low SWR so I dont damage my PA transistors and so that I can maximize power transfer to the antenna.


    (Yes I know I can use a directional coupler but I would like to have a standalone instrument with acceptable accuracy that I can use outside that also has a display. I dont need HF coverage as I have an antenna analyzer that cover HF).

    Wished spec:

    SWR reading continuously so I can adjust / tweak on the fly

    SWR Graph of a band of frequencies

    Battery operation

    Display

    Instrument used by several OMs already so I dont buy the first prototype


    Nice to have:

    R and X readout (not absolutely necessary)

    PC software

    USB


    I have seen some OMs use this one:

    https://www.banggood.com/N1201…983.html?cur_warehouse=CN


    But are there better alternatives? What are your experiences? Please share your comments.

    S59MZ in the first picture there seems to be two capacitors? Is this in unmodified state?


    In the second picture, there seems that you have moved one of the caps to the other side (moved to upper side in picture) so it is in series with the injected signal there. But there seems to still be the one capacitor there in addition still?


    Can draw a quick schematic of your mod and how you changed the capacitors as well as where you did inject the signal? What PLL chip is on that LNB?

    What GPS module do you recommend for generating a stable 25 MHz signal or alternatively 10 MHz signal to stabilize LNB drift?


    I have done some experiments with uBlox 6. However, it appears to have max. 24 MHz out and it was sort of a hack taking the signal off the led output. I would like something more reproducible and I would like to avoid buying surplus GPSDO components off ebay.


    • What GPS modules / breakout modules do you have experience with? Example: Sparkfun, Adafruit etc...
    • Are there GPS modules from uBlox that can directly generate 25 MHz?
    • Are there better suited GPS modules than the series from uBlox (that doesnt cost a lot)?

    DL5MGD thanks for info about using Si5351. I see you replaced the default 25 MHz crystal oscillator, with a 10 MHz oscillator. Then I would assume the out frequency becomes too low is you dont tweak the settings.


    What settings did you do in software to be able to set the correct frequeny via SPI to the Si5351? I see you use the Etherkit/Si5151 library.


    Good morning,

    I am using here an Octagon Oslo Optima LNB and a sdr usb stick. As reference frequency source for both devices i made a small circuit from parts lying around which delivers 25MHz for the lnb and 28.8MHz for the sdr stick disciplined via gps. The arduino sketch is programmed in a very direct stile.....not very nice, but working. The sketch needs two libraries: https://github.com/mikalhart/TinyGPSPlus and https://github.com/etherkit/Si5351Arduino


    vy73

    DL5MGD

    Inside the LNB there is also a PLL and VCO as well as phase detector and loop filter (implemented in the PLL chip). Have someone actually checked the loopfilter and vco design of this internal PLL? I am wondering if this internal PLL / VCO combination may be causing the wobble we sometimes can hear on the beacon even with what should be quite stable reference? Is the loopfilter or other aspects of this loop modifiable?


    Have someone verified carefully that the LNB will be so stable listening on the CW beacon with an external OCXO or GPS locked OCXO

    ...that no wobble at all will be noticeable on the CW beacon?


    (After all we are locking a PLL to another PLL .... when we do this mod)


    (Just an idea)


    73

    DB8TF how do you connect the D75F to the LNB?


    Straight at the xtal input pin after removing the xtal, or do you need to adapt signal level via resistive divider for example?


    Also, do you need to have a capacitor between the D75F and the above mentioned xtal input pin?


    Has anone some pics of their LNB onboard D75F mod?


    73